Wafer-supporting device and method for producing same

ABSTRACT

A wafer-supporting device for supporting a wafer thereon adapted to be installed in a semiconductor-processing apparatus includes: a base surface; and protrusions protruding from the base surface and having rounded tips for supporting a wafer thereon. The rounded tips are such that a reverse side of a wafer is supported entirely by the rounded tips by point contact. The protrusions are disposed substantially uniformly on an area of the base surface over which a wafer is placed, wherein the number (N) and the height (H [μm]) of the protrusions as determined in use satisfy the following inequities per area for a 300-mm wafer:
 
(−0.5 N +40)≤ H ≤53;5≤ N ≤100.

BACKGROUND Field of the Invention

The present invention generally relates to a wafer-supporting device installed in a semiconductor-processing chamber, particularly to a wafer-supporting device having protrusions for supporting a wafer thereon.

Description of the Related Art

One typical conventional susceptor has a flat surface as shown in FIG. 1A. A wafer-supporting device 1 is adapted to be attached to a susceptor base which typically includes a heater. A wafer is placed on the wafer-supporting device for processing typically by plasma enhanced CVD or ALD. As shown in FIG. 1A (the top figure is a plan view, and the bottom figure is a cross section view taken along line 1A-1A), the wafer-supporting device has a flat surface. However, when a wafer is placed on the flat surface and processed, generation and accumulation of particles are typically observed on a reverse side of the wafer after film formation. Further, depending on the type of processing, sticking of the reverse side of a wafer on the top surface of the wafer-supporting device often happens. In order to resolve the above problems, conventionally, there are two types of wafer-supporting devices developed. FIG. 1B (the top figure is a plan view, and the bottom figure is a cross section view taken along line 1B-1B), illustrates an emboss type wafer-supporting device 2 having convex portions 3 isolated by a continuous base surface. FIG. 1C (the top figure is a plan view, and the bottom figure is a cross section view taken along line 1C-1C) illustrates a dimple type wafer-supporting device 4 having concave portions 5 isolated by a continuous base surface. Although the convex portion shown in FIG. 1B is square-shaped as viewed from above, it can be circular. Likewise, although the concave portion shown in FIG. 1C is circular as viewed from above, it can be square-shaped.

In order to reduce the number of particles generated and attached on the reverse side of a wafer during film formation, reducing a contact area between the reverse side of a wafer and the top surface of a susceptor is generally effective. However, even when the emboss type or dimple type wafer-supporting device is used, generation and accumulation of particles on the reverse side of a wafer are still a problem. Further, the convex or concave portions of the wafer-supporting device also affect uniformity of film thickness and film properties.

Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.

SUMMARY

Consequently, in an aspect, an object of the present invention is to provide a susceptor top surface which can reduce the number of particles attached to the reverse side of a wafer during film formation, and also can improve uniformity of film thickness and film properties. Since particles are observed on the reverse side of a wafer where the reverse side of the wafer and the top surface of the wafer-supporting device are in contact with each other during film formation, in some embodiments, in order to reduce a contact area between the reverse side of a wafer and the top surface of the wafer-supporting device, protrusions having rounded tips are provided on a base surface of a wafer-supporting device so as to reduce the contact area. In the above, reducing the number of protrusions would be effective in order to reduce the number of contact points between the reverse side of a wafer and the top surface of a wafer-supporting device. However, when the number of protrusions is small, a wafer tends to undergo slight sagging or deformation between the contact points (even if it is a small degree) depending on the type of processing, thereby contacting the top surface of the susceptor and increasing generation and accumulation of particles on the reverse side of the wafer. In the above, it is possible to inhibit contact between the reverse side of the wafer and the top surface of the wafer-supporting device even when the slight sagging or deformation of the wafer occurs by increasing the height of the protrusions. However, when the height of the protrusions is increased, film stress tends to suffer.

In view of the above, in some embodiments, by using protrusions having rounded tips and using the number and the height of the protrusions as control parameters, the wafer-supporting device is designed, which can surprisingly reduce accumulation of particles on the reverse side of a wafer and can improve film properties such as film stress and uniformity of film thickness.

Some embodiments provide a wafer-supporting device for supporting a wafer thereon adapted to be installed in a semiconductor-processing apparatus, comprising: (i) a base surface; and (ii) protrusions protruding from the base surface and having rounded tips for supporting a wafer thereon, said rounded tips being such that a reverse side of a wafer is supported entirely by the rounded tips by point contact, said protrusions being disposed substantially uniformly on an area of the base surface over which a wafer is placed, wherein the number (N) and the height (H [μm]) of the protrusions as determined in use satisfy the following inequities per area for a 300-mm wafer: (−0.5N+40)≤H≤53, 5≤N≤100.

In another aspect, some embodiments provide a method for producing a wafer-supporting device for supporting a wafer thereon adapted to be installed in a semiconductor-processing apparatus, comprising: (I) providing a wafer-supporting device with a base surface; (II) designing protrusions using the following inequities per area for a 300-mm wafer; and (III) producing a wafer-supporting device with the designed protrusions: (−0.5N+40)≤H≤53, 5≤N≤100,

-   -   wherein N and H are the number and the height ([μm]) of the         protrusions as determined in use, respectively, said protrusions         protruding from the base surface and having rounded tips for         supporting a wafer thereon, said rounded tips being such that a         reverse side of a wafer is supported entirely by the rounded         tips by point contact, said protrusions being disposed         substantially uniformly on an area of the base surface over         which a wafer is placed.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic view of a conventional wafer-supporting device wherein the top figure is a plan view, and the bottom figure is a cross section view taken along line 1A-1A.

FIG. 1B is a schematic view of a conventional wafer-supporting device wherein the top figure is a plan view, and the bottom figure is a cross section view taken along line 1B-1B.

FIG. 1C is a schematic view of a conventional wafer-supporting device wherein the top figure is a plan view, and the bottom figure is a cross section view taken along line 1C-1C.

FIG. 2A is a schematic view of a wafer-supporting device according to an embodiment of the present invention where the top figure is a top view, the middle figure is a cross section view taken along line 2A-2A according to an embodiment, whereas the bottom figure is a cross section view taken along line 2A-2A according to another embodiment.

FIG. 2B is a schematic view of a wafer-supporting device according to another embodiment of the present invention where the top figure is a top view, the middle figure is a cross section view taken along line 2B-2B according to an embodiment, whereas the bottom figure is a cross section view taken along line 2B-2B according to another embodiment.

FIG. 2C is a schematic view of a wafer-supporting device according to still another embodiment of the present invention where the top figure is a top view, the middle figure is a cross section view taken along line 2C-2C according to an embodiment, whereas the bottom figure is a cross section view taken along line 2C-2C according to another embodiment.

FIG. 2D is a schematic view of a wafer-supporting device according to yet another embodiment of the present invention where the top figure is a top view, the middle figure is a cross section view taken along line 2D-2D according to an embodiment, whereas the bottom figure is a cross section view taken along line 2D-2D according to another embodiment.

FIG. 2E is a schematic view of a wafer-supporting device according to a different embodiment of the present invention where the top figure is a top view, the middle figure is a cross section view taken along line 2E-2E according to an embodiment, whereas the bottom figure is a cross section view taken along line 2E-2E according to another embodiment.

FIG. 3 is an image of Defect Review SEM (scanning electron microscope) of a scratched portion of a reverse side of a wafer after film formation using a wafer-supporting device having columnar protrusions having a diameter of 1 mm (as a comparative example).

FIG. 4 is an image of Defect Review SEM (scanning electron microscope) of a scratched portion of a reverse side of a wafer after film formation using a wafer-supporting device having sphere-top protrusions wherein the spheres having a diameter of 2 mm are embedded, according to an embodiment of the present invention.

FIG. 5 is an image of Defect Review SEM (scanning electron microscope) of a circular deformation portion of a reverse side of a wafer after film formation using a wafer-supporting device having sphere-top protrusions wherein the spheres having a diameter of 2 mm are embedded, according to an embodiment of the present invention.

FIG. 6 is a Particle Map (by a Wafer Surface Inspection System) of a reverse side of a wafer after film formation using a wafer-supporting device having columnar protrusions having a diameter of 1 mm and a height of 30 μm, wherein bright spots indicate adhesion of particles (as a comparative example).

FIG. 7 is a Particle Map (by a Wafer Surface Inspection System) of a reverse side of a wafer after film formation using a wafer-supporting device having sphere-top protrusions with a height of 50 μm wherein the spheres having a diameter of 2 mm are embedded, wherein bright spots indicate adhesion of particles, according to an embodiment of the present invention.

FIG. 8 is a graph illustrating the relationship between the film stress and the height of protrusions according to embodiments of the present invention.

FIG. 9 is a graph illustrating the relationship between the number of particles on a reverse side of a wafer and the height of protrusions according to embodiments of the present invention.

FIG. 10 is a graph illustrating the relationship between the height of protrusions and the number of protrusions in terms of film stress and the number of particles according to embodiments of the present invention.

FIG. 11 is a graph illustrating the relationship between the uniformity of film thickness and the height of protrusions (as a reference example).

FIG. 12 is a graph illustrating the relationship between the film stress and the height of protrusions (as a reference example).

FIG. 13 is a schematic view of a semiconductor-processing apparatus provided with a wafer-supporting device according to an embodiment of the present invention.

FIG. 14 is a Particle Map (by a Wafer Surface Inspection System) of a reverse side of a wafer after film formation using a wafer-supporting device having sphere-top protrusions with a height of 10 μm wherein the spheres having a diameter of 2 mm are embedded, wherein bright spots indicate adhesion of particles (as a comparative example).

FIG. 15 is a Particle Map (by a Wafer Surface Inspection System) of a reverse side of a wafer after film formation using a wafer-supporting device having sphere-top protrusions with a height of 30 μm wherein the spheres having a diameter of 2 mm are embedded, wherein bright spots indicate adhesion of particles (as a comparative example).

FIG. 16 is a Particle Map (by a Wafer Surface Inspection System) of a reverse side of a wafer after film formation using a wafer-supporting device having sphere-top protrusions with a height of 32 μm wherein the spheres having a diameter of 2 mm are embedded, wherein bright spots indicate adhesion of particles (as a comparative example).

FIG. 17 is a graph illustrating the relationship between height H [μm] of protrusions and the number (N) of protrusions wherein the gray area represents the range significantly improving film properties and particle accumulation according to embodiments of the present invention.

DETAILED DESCRIPTION

In the disclosure, “substantially equal”, “substantially uniform”, or the like may refer to a difference recognized by a skilled artisan such as those of less than 10%, less than 5%, less than 1%, or any ranges thereof, for example. In the disclosure, “point contact” may refer to rigid surfaces of two discrete objects initially touching each other theoretically or substantially at one point where at least one of the surfaces is curved, or refer to a contact area which may be about 50 μm or less in diameter or about 20 μm or less in diameter. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments. In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, in the present disclosure, the numbers applied in specific embodiments can be modified by a range of at least ±50% in other embodiments, and the ranges applied in embodiments may include or exclude the endpoints.

As described above, in some embodiments, a wafer-supporting device for supporting a wafer thereon adapted to be installed in a semiconductor-processing apparatus, comprises: (i) a base surface; and (ii) protrusions protruding from the base surface and having rounded tips for supporting a wafer thereon, said rounded tips being such that a reverse side of a wafer is supported entirely by the rounded tips by point contact, said protrusions being disposed substantially uniformly on an area of the base surface over which a wafer is placed, wherein the number (N) and the height (H [μm]) of the protrusions as determined in use satisfy the following inequities per area for a 300-mm wafer: (−0.5N+40)≤H≤53; 5≤N≤100. FIG. 17 is a graph illustrating the above relationship, wherein the gray area represents the range significantly improving film properties and particle accumulation. In some embodiments, H is no more than about 50 μm.

The height (H) is defined as the distance from a top plane of the base surface (a reference plane) to the highest point of the protrusion (regardless of whether there is a recess around the protrusion) typically when the wafer-supporting device is in use, i.e., while processing a wafer placed on the wafer-supporting device in a chamber. In some embodiments, when ceramic or alloy balls are used to constitute protrusions, due to the differences in thermal expansion between the ceramic balls and the material including the base surface, the height of the protrusions is reduced by, e.g., about 10 μm when the wafer-supporting device is in use for processing a wafer at a temperature of e.g., about 400° C. as compared with the height of the protrusions prior to the process. In some embodiments, when H′ is defined as the height of the protrusions when the wafer-supporting device is not in use, the inequities (−0.5N+50)<H′<65; 5<N<100 are satisfied. In some embodiments, when ceramic or alloy balls are used to constitute protrusions, H=(H′−10 μm). In some embodiments, H′ is at least (−0.5N+52.3), and no more than 60 μm. When the protrusions are formed by mechanically grinding a surface of the material of the wafer-supporting device, since there is no issue of difference in thermal expansion, the height of the protrusions when in use is substantially the same as that when in non-use, i.e., H=H′.

When ceramic or alloy balls are used to constitute protrusions, H (the height in use at a processing temperature) can be determined from H′ (the height in non-use at room temperature) as follows: When the wafer-supporting device is heated to T₁ from room temperature T₀, the depth of the void or recess accommodating the ball therein in the base surface increases by A: A=CTE(M)×D(M)×(T ₁ −T ₀)

wherein CTE(M) is the line thermal expansion coefficient of the base material of the wafer-supporting device, and D(M) is the diameter of the void or recess.

Likewise, when the ball is heated at T₁ from room temperature T₀, the diameter of the ball increases by B: B=CTE(B)×D(B)×(T ₁ −T ₀)

wherein CTE(B) is the line thermal expansion coefficient of the ball, and D(B) is the diameter of the ball. Thus: H=H′−(A−B)

For example, when the ball is made of sapphire (CTE(B)=7E−6), the base material is aluminum alloy 6061 (CTE(M)=23E−6), the diameter of the ball and the void or recess is 0.002 m (D(B)=D(M)=0.002), and T₁ is 400 (T₁=400° C., T₀=25° C.), the value of (A−B) can be calculated at 12.0E-6 [m]. When the diameter of the ball and the void or recess is 0.004 m (D(B)=D(M)=0.004) under the same conditions as above, the value of (A−B) can be calculated at 24.0E−6 [m].

In some embodiments, N is an integer of about 20 to about 40. In some embodiments, N is 21 or more, but less than 60. According to the configurations, films such as silicon oxide films formed from TEOS using the wafer-supporting device can have stable stress (deviations of film stress between wafers can be inhibited, e.g., within about 20 MPa or about 10 MPa), and the number of particles attached on the reverse side of a wafer can be reduced to about 400 or less or about 200 or less per area for a 300-mm wafer. In some embodiments, the wafer-supporting device does not include a heating element or a discrete electrode, or does not have any structures required for or serving as an electric chuck. In some embodiments, the wafer-supporting device includes a heating element and/or a discrete electrode without any structures required for or serving as an electric chuck.

In some embodiments, because the reverse side of a wafer and the rounded tips of the protrusions touch each other by point contact, an initial contact area (prior film formation) therebetween is extremely small, e.g., a range of 10⁻⁶% to 10⁻³% (in some embodiments, 10⁻⁵% to 10⁻⁴%) relative to the area of the reverse side of the wafer.

In some embodiments, the protrusions disposed on a diametric line of the base surface are arranged at substantially equal intervals. In some embodiments, the protrusions are disposed in a geometric arrangement on the base surface such that each one of the protrusions constitutes a point of each of identical squares or identical regular triangles formed by the protrusions. Alternatively, in some embodiments, the protrusions are disposed concentrically. Alternatively, in some embodiments, the protrusions are disposed in a geometric arrangement on the base surface such that each one of the protrusions constitutes a point of each of identical regular hexagons formed by the protrusions. In some embodiments, any of the foregoing configurations can be used in any combination on a single base surface.

In some embodiments, the protrusions are formed of ceramic balls embedded in the base surface. In some embodiments, the ceramic balls are made of sapphire. In some embodiments, the ceramic balls are made of alumina, other aluminum oxide, aluminum nitride, magnesium nitride, silicon carbon, or the like. In some embodiments, the protrusions are formed of dome-shaped ceramics. In some embodiments, stainless steel, aluminum alloy, titanium alloy, or the like may be used. In some embodiments, the rounded tips have a radius of about 1 mm to about 2 mm. In some embodiments, the ceramic balls have a diameter of about 2 mm to about 4 mm.

In some embodiments, the protrusions are formed of a material which is the same as that of the base surface. The base surface may be made of aluminum, anodic aluminum oxide, aluminum alloy, or the like.

In some embodiments, no protrusions other than the protrusions for supporting a wafer are provided on the base surface. In some embodiments, the base surface has no steps, spacers, or rims other than the protrusions, or no clamping mechanism. In some embodiments, the wafer is placed on the protrusions predominantly or substantially by gravity.

Another aspect of the present invention provides a semiconductor-processing apparatus comprising: (I) a reaction chamber capable of being evacuated; (II) a susceptor including any of the foregoing wafer-supporting devices and a heating block, which is installed inside the reaction chamber; and (III) a showerhead installed inside the reaction chamber in parallel with the susceptor. In some embodiments, the wafer-supporting device is used as a susceptor in a CVD apparatus including a plasma or thermal CVD apparatus, an ALD apparatus including a plasma or thermal ALD apparatus, or an etching apparatus. In some embodiments, the semiconductor-processing apparatus further comprises an RF power source wherein the susceptor and the showerhead serve as lower and upper electrodes for generating a plasma.

In still another aspect the present invention provides a method for producing a wafer-supporting device for supporting a wafer thereon adapted to be installed in a semiconductor-processing apparatus, comprising: (a) providing a wafer-supporting device with a base surface; (b) designing protrusions using the following inequities per area for a 300-mm wafer; and (c) producing a wafer-supporting device with the designed protrusions: (−0.5N+40)≤H≤53; 5≤N≤100, wherein N and H are the number and the height ([μm]) of the protrusions as determined in use, respectively, said protrusions protruding from the base surface and having rounded tips for supporting a wafer thereon, said rounded tips being such that a reverse side of a wafer is supported entirely by the rounded tips by point contact, said protrusions being disposed substantially uniformly on an area of the base surface over which a wafer is placed.

In some embodiments, the inequities are: (−0.5N+X)<H<Y; 5<N<100, wherein X=40.5, 41, 42, 43, 44, or 45, and Y=47, 48, 49, 50, 51, or 52 in any combination. In some embodiments, N is an integer of about 20 to about 40. In some embodiments, N is 21 or more, but less than 60.

The present invention will be explained in detail with reference to embodiments and drawings which are not intended to limit the present invention.

FIG. 2A is a schematic view of a wafer-supporting device 10 according to an embodiment of the present invention where the top figure is a top view, the middle figure is a cross section view taken along line 2A-2A according to an embodiment, whereas the bottom figure is a cross section view taken along line 2A-2A according to another embodiment. In this embodiment, protrusions 11, 11′ are disposed in a geometric arrangement throughout the base surface such that each one of the protrusions constitutes a point of each of identical squares formed by the protrusions. The protrusions 11, 11′ disposed on a diametric line (2A-2A) of the base surface are arranged at substantially equal intervals. The protrusions 11 are ceramic balls embedded in the base surface, whereas the protrusions 11′ are formed of a material which is the same as that of the base surface. The ceramic balls 11 can be embedded in the base surface by caulking. For example, the caulking method disclosed in JP 2007-180246 can be used, the disclosure of which is herein incorporated by reference in its entirety. The protrusion 11′ can be formed mechanically, e.g., by grinding. A wafer-supporting device 12 and protrusions 13, 13′ shown in FIG. 2B are similar to those shown in FIG. 2A, except that the number of the protrusions 11, 11′ in FIG. 2A is 21, whereas the number of the protrusions 13, 13′ in FIG. 2B is 37.

A wafer-supporting device 16 and protrusions 17, 17′ shown in FIG. 2D are similar to those shown in FIG. 2A, except that the number of the protrusions 11, 11′ in FIG. 2A is 21, whereas the number of the protrusions 17, 17′ in FIG. 2D is 22, and that the protrusions 17, 17′ are disposed in a geometric arrangement throughout the base surface such that each one of the protrusions constitutes a point of each of identical regular triangles formed by the protrusions. In the configurations shown in FIG. 2D, the distance between any and every two adjacent protrusions is the same, so that they can support a wafer more evenly, without causing sagging.

A wafer-supporting device 18 and protrusions 19, 19′ shown in FIG. 2E are similar to those shown in FIG. 2A, except that the protrusions 19, 19′ are disposed concentrically (the number of the protrusions 19, 19′ in FIG. 2E is 21 which is the same as in FIG. 2A).

A wafer-supporting device 14 and protrusions 15, 15′ shown in FIG. 2C are similar to those shown in FIG. 2A, except that the number of the protrusions 11, 11′ in FIG. 2A is 21, whereas the number of the protrusions 15, 15′ in FIG. 2C is 54, and that the protrusions 15, 15′ are disposed in a geometric arrangement throughout the base surface such that each one of the protrusions constitutes a point of each of identical regular hexagons formed by the protrusions. Also, the protrusions 15, 15′ disposed on a diametric line of the base surface are not arranged at equal intervals, but are arranged at two different intervals (alternately long intervals and short intervals).

FIG. 13 is a schematic view of a semiconductor-processing apparatus provided with a wafer-supporting device according to an embodiment of the present invention. In a reaction chamber 111, a susceptor top plate 101 includes a heating element 113 which is capable of moving up and down. A showerhead 102 is disposed above the wafer-supporting device 101 in parallel. The showerhead 102 and the wafer-supporting device 101 are capacitively coupled and serve as upper and lower electrodes. An RF power source 105 supplies RF power to the showerhead 102 and the wafer-supporting device is grounded at a grounding connection 112. To the showerhead 102, a precursor is supplied via a line 108 provided with a valve 103, whereas a reactant or other gases are supplied via a line 109 provided with a valve 104. The reaction chamber has an exhaust system (not shown).

EXAMPLES Comparative Example 1

A silicon oxide film having a thickness of about 350 nm was deposited using TEOS on a 300-mm wafer using the semiconductor-processing apparatus illustrated in FIG. 13 in which a wafer-supporting device (made of an aluminum alloy) having 17 columnar protrusions having a diameter of 1.0 mm concentrically distributed was installed and having a height (H′) of 50 μm (since the protrusions were mechanically formed, the height in use (H) was determined to be the same as the height in non-use (H′)). After the film formation, the reverse side of the wafer was observed. FIG. 3 is an image of Defect Review SEM (scanning electron microscope) of a scratched portion of the reverse side of the wafer after the film formation. As shown in FIG. 3, many areas of large scratches, some of which had a length of 1 mm or more and a width of 50-100 μm, were observed in areas generally where the tips of the protrusions were positioned. Further, as shown in FIG. 6 which is a Particle Map (by a Wafer Surface Inspection System) of the reverse side of the wafer after the film formation wherein bright spots indicate adhesion of particles, accumulation of particles was observed where 247 particles having a diameter of 0.2 μm or more were observed.

Example 1

Film formation was conducted on a wafer in the same manner as in Comparative Example 1, except that a wafer-supporting device illustrated in FIG. 2B (37 protrusions) using sapphire balls having a diameter of 2 mm and a height (H′) of 50 μm (H=38 μm) was used. Due to the differences in thermal expansion coefficient between the aluminum alloy body and the sapphire balls, the height in use (H) was determined to be about 12 μm shorter than the height in non-use (H′) as calculated below: A=CTE(M)(23E-6: aluminum alloy 6061)×D(M)(0.002 m)×(T ₁ −T ₀)(T ₁=390° C.,T ₀=25° C.)=17.0E-6 m B=CTE(B)(7E-6: aluminum alloy 6061)×D(M)(0.002 m)×(T ₁ −T ₀)(T ₁=390° C.,T ₀=25° C.)=5.18E-6 m A−B=11.8E-6 m H=H′−11.8 [μm] (≈12 μm).

FIG. 4 is an image of Defect Review SEM (scanning electron microscope) of a scratched portion of the reverse side of the wafer after the film formation. FIG. 5 is an image of Defect Review SEM (scanning electron microscope) of a circular deformation portion of the reverse side of the wafer after the film formation. As shown in FIGS. 4 and 5, although scratches and circular deformation portions were observed, they were very small and confined to small areas in a range of about 20 μm to about 30 μm in diameter. Further, as shown in FIG. 7 which is a Particle Map (by a Wafer Surface Inspection System) of the reverse side of the wafer after the film formation wherein bright spots indicate adhesion of particles, significantly less accumulation of particles was observed as compared to Comparative Example 1, where 112 particles having a diameter of 0.2 μm or more were observed.

Example 2

Film formation was conducted on a wafer in the same manner as in Example 1, except that a wafer-supporting device illustrated in FIG. 2A (21 protrusions) using sapphire balls having a diameter of 2 mm, and a wafer-supporting device illustrated in FIG. 2B (37 protrusions) using sapphire balls having a diameter of 2 mm were used, and the height (H′) of these wafer-supporting devices was changed as shown in FIG. 8, and film stress of the films was measured (due to the differences in thermal expansion coefficient between the aluminum alloy body and the sapphire balls, the height in use (H) was determined to be about 12 μm shorter than the height in non-use (H′)). FIG. 8 is a graph illustrating the relationship between the film stress and the height (H′) of protrusions according to this embodiment. The stress was the average of seven films, and the data when the height (H′) was 40 μm or less were obtained using the wafer-supporting device illustrated in FIG. 2A, and the data when the height (H′) was over 40 μm were obtained using the wafer-supporting device illustrated in FIG. 2B. As shown in FIG. 8, when the height (H′) of the protrusions is less than about 60 μm or about 65 μm (H< about 48 or 53 μm), deviations of film stress can be reduced within about 10 MPa.

Example 3

Film formation was conducted on a wafer in the same manner as in Example 1, except that a wafer-supporting device illustrated in FIG. 2A (21 protrusions) using sapphire balls having a diameter of 2 mm, and a wafer-supporting device illustrated in FIG. 2B (37 protrusions) using sapphire balls having a diameter of 2 mm were used, and the height (H′) of these wafer-supporting devices was changed as shown in FIG. 9, and the number of particles on the reverse side of the wafer was measured. FIG. 9 is a graph illustrating the relationship between the number of particles on a reverse side of a wafer and the height (H′) of protrusions according to this embodiment. The number of particles was the average of three wafers. As shown in FIG. 9, when the height (H′) of the protrusions illustrated in FIG. 2A (21 protrusions) was no less than about 40 μm (H< about 28 μm), the number of particles having a diameter of 0.2 μm or larger could be controlled to under about 500, and when the height (H′) of the protrusions (21 protrusions) was more than about 40 μm (H> about 28 μm), the number of particles having a diameter of 0.2 μm or larger could be controlled to under about 300, whereas when the height (H′) of the protrusions illustrated in FIG. 2B (37 protrusions) was more than 30 μm (H> about 18 μm), the number of particles having a diameter of 0.2 μm or larger could be controlled to under about 300. For both the protrusions illustrated in FIG. 2A (21 protrusions) and the protrusions illustrated in FIG. 2B (37 protrusions), it is expected that when the height (H′) of the protrusions is about 50 μm or more (H> about 38 μm), the number of particles can be reduced to less than about 200.

FIG. 14 is a Particle Map (by a Wafer Surface Inspection System) of the reverse side of the wafer after the film formation using the wafer-supporting device having 21 sphere-top protrusions with a height (H′) of 10 μm (H≈0 μm) wherein bright spots indicate adhesion of particles (as a comparative example). When the sapphire balls were used, the height in use (H) was determined to be about 12 μm shorter than the height in non-use (H′), and thus, the height (H′) of 12 μm was determined to be nearly full contact. FIG. 15 is a Particle Map (by a Wafer Surface Inspection System) of the reverse side of the wafer after the film formation using the wafer-supporting device having 21 sphere-top protrusions with a height (H′) of 30 μm (H=18 μm) wherein bright spots indicate adhesion of particles (as a comparative example). FIG. 16 is a Particle Map (by a Wafer Surface Inspection System) of the reverse side of the wafer after the film formation using the wafer-supporting device having 21 sphere-top protrusions with a height (H′) of 32 μm (H=20 μm) wherein bright spots indicate adhesion of particles (as a comparative example). For the wafer-supporting devices having 21 protrusions (sapphire balls), when the height (H′) was 32 μm or less (H<20 μm), it is revealed that the reverse side of the wafer, by sagging, came into contact with the base surface of the wafer-supporting device in the areas between the protrusions (there were fewer particles around the protrusions) during the film formation, thereby increasing accumulation of particles on the reverse side of the wafer.

Reference Example 1

Film formation was conducted on a wafer in the same manner as in Comparative Example 1, except that the height of the protrusions was changed. FIG. 11 is a graph illustrating the relationship between the uniformity of film thickness and the height of protrusions. FIG. 12 is a graph illustrating the relationship between the film stress and the height of protrusions. Since the protrusions were mechanically formed, the height in use (H) was determined to be the same as the height in non-use (H′). As shown in FIGS. 11 and 12, when the height of the protrusions was more than about 60 μm, not only film stress, but also uniformity of film thickness, suffered. FIG. 12 corresponds to FIG. 8, and thus, it is expected that also when the wafer-supporting device having sphere-top protrusions is used, uniformity of film thickness will suffer when the height of the protrusions is more than about 60 μm.

Relationship Between Number of Protrusions and Height

Through experiments, it can be determined that on the average, two particles having a diameter of 0.2 μm or more are generated and attached to a reverse side of a wafer per protrusion. Thus, when the number of protrusions is no more than about 100, the number of particles is expected to be no more than about 200. Further, when the number of protrusions is increased, the cost of producing a wafer-supporting device also increases. In view of the above, and the foregoing examples, FIG. 10 is a graph illustrating the relationship between the height (H′) of protrusions and the number of protrusions for significantly improving film stress and the number of particles. In FIG. 10, “N/G” denotes not good or poor, “OK” denotes acceptable or satisfactory, “Gray” denotes a range between poor and acceptable, and “OK B/L” denotes borderline acceptable.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

What is claimed is:
 1. A wafer-supporting device for supporting a wafer thereon adapted to be installed in a semiconductor-processing apparatus, comprising, without any structures required for or serving as an electric chuck: a base surface comprising an embedded heating element for heating the base surface; and protrusions protruding from the base surface and having mechanically ground rounded tips for contacting and supporting a wafer thereon, said rounded tips being such that a reverse side of a wafer is supported entirely by the rounded tips by point contact wherein a total area of the rounded tips of the protrusions contacting the reverse side of the wafer is in a range of 10⁻⁶% to 10⁻³% of the area of the reverse side of the wafer, said protrusions being entirely formed of a material which is the same as that of the base surface, which material is aluminum, anodic aluminum oxide, or aluminum alloy, so that there is no difference in thermal expansion between the protrusions and the base surface, and being integrally formed mechanically by mechanical grinding of the base surface and distributed substantially uniformly on an area of the base surface over which a wafer is placed, wherein the number (N) and the height (H [μm]) of the protrusions as determined in use satisfy the following inequalities per area as measured for a 300-mm wafer: (−0.5N+40)≤H≤53 20≤N≤40 said wafer-supporting device having no clamping mechanism, so as to retain the wafer on the protrusions substantially solely by gravity when in use, wherein the protrusions disposed on a diametric line of the base surface are arranged at substantially equal intervals, wherein the base surface and the heating element are configured to move up and down; and wherein the wafer-supporting device is grounded.
 2. The wafer-supporting device according to claim 1, wherein the protrusions are disposed in a geometric arrangement on the base surface such that each one of the protrusions constitutes a point of each of identical squares or identical regular triangles formed by the protrusions.
 3. The wafer-supporting device according to claim 1, wherein the protrusions are formed of dome-shaped ceramics.
 4. The wafer-supporting device according to claim 1, wherein the rounded tips have a radius of about 1 mm to about 2 mm.
 5. A semiconductor-processing apparatus comprising: a reaction chamber capable of being evacuated; a susceptor including the wafer-supporting device of claim 1 and a heating block, which is installed inside the reaction chamber; and a showerhead installed inside the reaction chamber in parallel with the susceptor.
 6. The semiconductor-processing apparatus according to claim 5, further comprising an RF power source wherein the susceptor and the showerhead serve as lower and upper electrodes for generating a plasma. 